Pesticides kill frogs, new research

Pesticides, fully authorised by the relevant authorities, and used in recommended amounts can lead to mortality rates of up to 100 percent on amphibians according to a new study in Germany.

January 2013. A recent study has revealed that even the use of the recommended amount of agrochemicals can lead to mortality rates of 20 to 100 percent in common frogs (Rana temporaria). The study tested the risk of seven different chemicals; fungicides, herbicides and insecticides, and all were found to be damaging or lethal to frogs. However, the chemicals are still allowed because the testing methods did not check their effects on amphibians. The study was commissioned by the Federal Environment Agency and conducted by the Institute of Environmental Sciences Landau at the University of Koblenz-Landau.

“It’s hard to comprehend that the pesticides have gone through the current authorization process but are still a direct threat to amphibians,” said Carsten Brühl, who led the study. “Our laboratory tests show the effect on fully formed frogs, rather than tadpoles”.

The tests that were conducted on these chemicals were undertaken on amphibians in the aquatic habitat, and mostly on tadpoles. The serious effects that are found mostly effect the land-based frog and toad populations were not taken into account.

The moist skin of frogs absorb pesticides in large quantities

Amphibians are the most threatened vertebrates worldwide. Possible causes of the decline of amphibians worldwide are thought to be competition with invasive species, increased ultraviolet radiation, global warming, infectious diseases and the loss of habitat. However, the impact of pesticides has not previously been suspected. This is because the evaluation of possible effects of pesticides had been inadequately tested and was not part of the authorization procedure for agrochemical products. Currently, only the effects on birds and mammals and aquatic organisms are tested.

Dangerous to birds and mammals

Even in birds and mammals, there has long been a discussion of whether pesticides are absorbed through the skin and how big the consequent risk is. The moist skin of frogs absorbs substances in much greater quantities, as it is in direct contact with the environment. So the danger of so-called dermal exposure is high.

Fatal to 100 percent

This attitude and testing process needs to be fundamentally rethought. The study tested recommended amounts of a fungicide named “Headline” on juvenile grass frogs and within an hour it lead to a mortality rate of 100 per cent. However, tests under different conditions, containing the same amount of the active substance, killed only 20 percent; the risk is probably in the additives used in each case or in the concentration used. Which substances are dangerous and how they work is still unclear and requires further research. This also applies to the potential effects of pesticides on rural populations.

Urgent action required

“Our study shows that urgent action is now,” said Carsten Brühl. “Even farmers have an interest in conserving amphibians, as they are a key ally in destroying harmful insects. It is therefore imperative to use pesticides that do not endanger them.”
Likewise pesticide risk assessment managers must deal with this issue and include land based amphibians in their analysis.